The present disclosure relates to a variable differential transformer for measuring the movement of an object.
The linear variable differential transformer (LVDT) is one of the oldest electronic methods known to accurately measure the linear displacement of a body. The LVDT is a differential transformer which consists of a primary winding and two secondary windings and a movable coupling core.
As shown in FIGS. 1-3 a LVDT device 10 of the prior art (e.g., movable coupling core) is shown. Here LVDT device 10 comprises a primary winding 12, a first secondary winding 14, a second secondary winding 16 and a movable core 18. As is known in the related arts the core is connected to a sine wave excitation source for inducing voltages in the secondary windings.
When the movable core is at a center point of travel (FIG. 1) the core equally overlaps the two secondary windings, which results in equal voltages being induced in the secondary windings. The two secondary windings are connected in such a way that the two voltages are opposite in phase and cancel each other out resulting in a zero output. This is illustrated schematically in graph 20.
As the core moves to the maximum point of travel in one direction (FIG. 2) the induced voltage reaches a maximum with a phase illustrated in graph 22. This is because the core, which is of a high permeability material couples more magnetic flux into secondary winding 14 and very little into secondary winding 16. The difference between secondary winding 14 and secondary winding 16 results in a maximum amplitude and phase graph 22, which is similar to the excitation. Positions of the core between the center of travel illustrated in FIG. 1 and the maximum illustrated in FIG. 2 will have a lower amplitude but similar phase.
As the core moves to the position illustrated in FIG. 3. the amplitude of the induced voltage reaches a maximum (graph 24), with a phase that is 180 degrees opposite to the phase of graph 22. FIG. 4 schematically illustrates a LVDT 10. As illustrated in FIG. 4, the windings and the movable core are housed with a structure and movement of the movable core is facilitated by an actuating member 28 that is secured to the movable core at one end and the item whose movement is to be tracked or sensed at the other end. In order to allow for movement of the movable core the actuating member must pass through a sealing device or bearing that allows for movement of the actuating member while protecting the interior of the LVDT from contamination, such as moisture or salt or other contaminants which may affect performance of the LVDT.
Examples of such LVDTs are disclosed in U.S. Pat. Nos. 3,546,648 and 4,808,958 the contents of which are incorporated herein by reference thereto.
There are two shortcomings of the LVDTs of the prior art that are overcome by the present disclosure. First, the length of the LVDT device is twice the designed length of travel since the actuating member must have a length outside of the housing that is long enough to provide the movement illustrated in FIGS. 1-3 (e.g., movement of the core within the housing). And secondly, the actuating member or rod, which is secured to the movable core and the body to be measured, must pass through the housing of the LVDT which means a sealing means is required.
In vehicular applications these two problems are exacerbated as real estate for such devices is typically at a premium and sealing means which are subject to constant movement may curtail the life expectancy of such a device.
A magnetically variable differential transformer, comprising: a primary winding; a first secondary winding; a second secondary winding; a non-movable permeable core disposed within the primary winding, the first secondary winding and the second secondary winding; and a movable magnet configured for movement about the primary winding, the first secondary winding and the second secondary winding, wherein movement of the movable magnet causes magnetic saturation of portions of the non-movable permeable core.
A magnetically variable differential transformer, comprising: a primary winding disposed on a center portion of a bobbin having a central opening, the bobbin being formed out of a non-magnetic material; a first secondary winding disposed on one side of the bobbin adjacent to the primary winding; a second secondary winding disposed on another side of the bobbin adjacent to the primary winding; a non-movable permeable core being disposed in the central opening and being disposed within the first secondary winding, the primary winding and the second secondary winding; and a movable magnet disposed about the primary winding, the first secondary winding and the second secondary winding, wherein movement of the movable magnet causes magnetic saturation of portions of the non-movable permeable core.
A magnetically variable differential transformer, comprising: a primary winding disposed about a center portion of a non-movable permeable core; a first secondary winding disposed on one side of the primary winding and being disposed about a first portion of the non-movable permeable core; a second secondary winding disposed on another side of the primary winding and being disposed about a second portion of the non-movable permeable core; and a movable magnet being configured to magnetically saturate one of the first portion, the second portion or the center portion of the non-movable permeable core as the movable magnet moves with respect to the non-movable permeable core.
A method for tracking the movement of a movable object with a variable differential transformer, comprising: providing an excitation to a primary winding disposed between a first secondary winding and a second secondary winding, the primary winding, the first secondary winding and the second secondary winding are each disposed about a non-moveable permeable core, wherein the first secondary winding and the second secondary winding are connected to each other and provide an output corresponding to voltages induced within the first secondary winding and the second secondary winding by the primary winding; and coupling a movable magnet to the movable object wherein the movable magnet saturates portions of the non-moveable permeable core thereby modifying the output corresponding to voltages induced within the first secondary winding and the second secondary winding by the primary winding.